Definition

By: Gregory R. Waryasz, MD

The extensor indicis muscle of the musculoskeletal system is characterized by passing through extensor compartment four along with the extensor digitorum.

It is part of the forearm.  It consists of skeletal muscle fibers.

Its unique structural features include its tendon passing with the extensor digitorum in the fourth extensor compartment through the tendinous sheath of the extensor digitorum and extensor indicis.  The muscle is narrow and elongated.

The origin is the posterior surface of the distal third of the ulna and interosseous membrane.

The insertion is the extensor expansion of the 2nd finger.

The blood supply is from the posterior interosseous artery and venous drainage is from the accompanying veins.

The innervation is from the posterior interosseous nerve.

The extensor indicis muscle as well as all other bones, muscles, and ligaments of the body are derived of mesodermal origin in the embryo.

The function of the extensor indicis is to extend the 2nd finger. It also helps with extending the hand at the wrist joint. The synergist is the extensor digitorum.

Common diseases include tendon rupture.

Tendon rupture can occur from trauma.

Commonly used diagnostic procedures include clinical history, physical exam, and MRI.

It is usually treated with splinting or surgery depending upon the mechanism of injury.

References

Lieberman J (ed), AAOS Comprehensive Orthopaedic Review, American Academy of Orthopaedic Surgeons, 2008.

Moore K, Dalley A (eds), Clinically Oriented Anatomy (5th edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.

Wheeless’ Textbook of Orthopaedics: Extensor Indicis (http://www.wheelessonline.com/ortho/extensor_indicis)